BAGRAM AIR FIELD, Afghanistan - President Barack Obama slipped unannounced into dangerous Afghanistan on Friday, one year after widening an ever deadlier war and just days before a pivotal review about the 9-year-plus conflict.

Under intense security, Obama landed in night's darkness after a clandestine departure from the White House on Thursday, where plans of his trip into the war zone were tightly guarded. He was to spend up to six hours in Afghanistan, meeting with President Hamid Karzai in the capital and with troops at giant Bagram Air Field, the main U.S. base here. Obama also was to talk with Gen. David Petraeus, the top U.S. and NATO war commander in Afghanistan, and Karl Eikenberry, the U.S. ambassador to Afghanistan.

Obama's trip was meant to show personal resolve toward ending a war that was launched in the weeks after the Sept. 11, 2001, attacks and is now raging in its 10th year, making it the longest U.S. conflict other than Vietnam.

He also wanted to personally thank the troops at a time when millions back home are thinking of holiday peace, not war. This has been the deadliest year to date for U.S. forces in Afghanistan. More than 450 have been killed in 2010.